The present invention relates to an etchant for etching silicon nitride and borosilicate glasses, and a method of etching through superimposed layers of silicon nitride and borosilicate glasses.
In making semiconductor devices it is the practice to passivate or protect the surface of a body of semiconductor material with a layer or superimposed layers of inorganic insulating materials. The materials generally used for this purpose include silicon dioxide, silicon nitride and borosilicate glasses. One type of protection system used includes a layer of a borosilicate glass over a layer of silicon nitride. Also, a layer of silicon dioxide is often used between the silicon nitride layer and the semiconductor body.
It is often desirable to provide openings through the protection layer or layers to the semiconductor body. Such openings are usually formed by applying a photoresist mask on the outermost layer of the protection system with the mask having openings therethrough where the openings in the protection system are desired. The uncoated regions of the protection system are then removed with a suitable etchant. Where the protection system comprises superimposed layers of different materials, it is desirable to use an etchant which will remove the materials of all of the layers so as to simplify the etching operation. Also, it is desirable that, although the etchant readily attacks the materials of the protection system, the etchant should not attack the photoresist.
Various etchants have been developed for etching silicon nitride and silicon oxide. For example, U.S. Pat. No. 3,859,222, issued Jan. 7, 1975 to A. S. Squillace et al, entitled "Silicon Nitride-Silicon Oxide Etchant" discloses an etchant consisting of a mixture of phosphoric acid and a fluoborate anion for etching silicon nitride and silicon oxide. However, the etchants for silicon nitride, including that of U.S. Pat. No. 3,859,222, do not also etch borosilicate glasses.